An ICM poll for the News of the World newspaper put the Conservative Party's lead over Labour at nine points, up three since the same survey was conducted two weeks ago.
It is the first time for over two weeks that the Conservatives have managed to attract 40% of the vote.
A poll last weekend said their lead had been cut to just two percentage points, unnerving the Conservative hierarchy and financial markets.
Uncertainty about the outcome of the election helped push sterling to a 10-month low against the dollar a day after the poll drop, as currency markets fretted about whether the next government would be able to tackle the growing debt burden.
The ICM poll on Sunday put Labour up one on 31% of the national vote and the Liberal Democrats down two on 18%.
Replicated at a national election, widely expected to take place on 6 May, the ICM forecast would not give the Conservatives an overall majority, resulting in a hung parliament.
The paper predicted David Cameron's party would win 320 seats. Labour would win 260 with other parties gaining 80 seats, leaving Cameron short of an absolute majority.
A YouGov poll to be published in the Sunday Times also showed the Conservatives pulling away from Labour, but with a smaller lead than the ICM poll suggested.
The poll said the Conservatives' lead had risen to five points compared with a margin of just two points over Labour when it was conducted last weekend.
YouGov interviewed 1,558 adults on March 4 and March 5 for the Sunday Times, while ICM interviewed a sample of 1,005 adults on March 3 and 4.
(EurActiv with Reuters.)